[wiml]

The BBC isn't hosting anyone else on their instance (nor can I think of a reason they would want to). As I understand it it's just a way for their activity to be visible on the fediverse. That should make their infra costs minimal; they don't have moderation of comments/replies; and federation/defederation wars will only affect the specific other instances which choose to defederate from the BBC. Your third point is valid but that's why this is an experiment.

[dahwolf]

You may want to read the actual article which explains how replies very much end up on their instance and therefore require moderation. They will 100% host all replies + all media attached to it. That's how federation works.

Yes, defederation is per instance but cuts of all users of that instance from BBC. Here's a fresh example:

https://social.anoxinon.de/@[e-mail]/11080988949...

Pretty large instance that defederated before BBC even started.